Anamorphic cinematography lenses inherently have various amounts of astigmatism that must be corrected to create a sharp image. Methods of correction include use of two lenses to reduce astigmatism. The lenses are rotated to reduce the astigmatism.
Methods to rotate the lenses include a gear or cam to rotate the lenses. Using the gear method, the movement of the system is limited to a linear progression and does not achieve the most accurate results. The cam method relies on the use of return springs for one direction of rotation. The cam method lacks reliability because, due to environmental changes, the springs do not always have enough strength to overcome the resistance from the optical housings being driven and often fail. Further, springs may weaken over time and screws that attach the springs to the housings could loosen or back out. This method may also cause an inconsistent feel for the user due to increased spring tension at closer focus distances. Further, the close focus range is limited due to geometrical limitations of the system.